Caption: Human fossils, Sima de los Huesos. Hundreds of pieces of human fossils were found together in an area measuring 50x50 centimetres at Sima de los Huesos (Pit of Bones). It is thought that the site was used as a cemetery by early humans, 400,000 years ago. This population were remote ancestors of Neanderthal man and have been given the scientific name Homo heidelbergensis. Sima de los Huesos is one of several sites in Sierra de Atapuerca, Spain, that have been studied on and off over the past century, leading to a massive advancement in the understanding of human evolution. In 2000, Sierra de Atapuerca was made a world heritage site by UNESCO.